Ophthalmic glass



Patented Jan. 6, 1948 OPHTHALMIC o nss William H. Armistead, Corning, N. Y., assignor to Corning Glass Works, Corning, N. Y.,'a 001- r efi n 9 New erk No Drawing. Application August 19, 1946,

" Serial No. 691,663

This invention relates to transparent ophthal: mic glasses, small buttons of which .are to be sealed into lenses of crown glass for the pro- .duction of multifocal spectacle lenses. Glasses which are to be used for this purpose must meet certain requirements. Above all, they must seal properly with standard White optical crown glass which has a thermal expansion coeificient .of 93 10 cm. per cm. per degree C. and a softening point of about 725 C. Softening point is that temperature at which a fibre of the glass of specified size Will elongate under its own weight at a given rate when suspended through a small n eq pec fi dimens ons V scosi offelass between the strain pointand melting temperature, by H. R. Lillie, Jour. Am. Cer. Soc., vol. 14,;page 502, July 1931). They must have good .devitrification resistance during sealing and adequate chemical durability or resistance to Weathering. Their purpose requires anindex of refraction for the D line (nD) between 1.57 andIL'lO and it is desirable that they have a dispersive index 1;) which is as high as possible. Prior ophthalmic glasses of high refractive index have a maximum dispersive index ofabout 32 which isless than desired. The prior glasses of lower refractive index have a maximum dispersive index of about 50 but have insufficient chemical durability.

The primary object of this invention is to provide ophthalmic glasses which have higher dispersive indices than has hitherto been obtainable in glasses of this type without sacrifice of other desirable properties.

Another object is to provide ophthalmic glasses having optical properties ranging from nD=1.70, preferably nD=1.65, 2:46, to nD=1.5'7, preferably nD=1.59, 11:53, but having at the same time good chemical durability, softenin points below 700 C. and thermal expansion coefficients between 83 and 95 10- cm. per cm. per degree C.

In general I have found that the above objects may be attained with glasses comprising 33% to 60% $102, 1% t 7% B203, 4% to 15% ZrOz, 0% to 25% BaO, 3% to 15% ZnO, .5% to Li2O, and 1% to Na2O. In lieu of NazO, K may be substituted wholly or in part. Although BaO may be absent, the glass preferably should contain at least 5% thereof because BaO raises the refractive index without unduly lowering the dispersive index. More than BaO may cause devitrification. Other oxides, if desired, may be added with benefit as follows:

CaO raises the refractive index, although on a is particularly valuable for further increasing the refractive index without causin devitrification in glasses having large BaO contents, but it may also be added .to the glass irrespective of the presence .or absence of BaO. Up to 15% CaO may .thus be employed.

Up to 8% A1203 may be added, preferably but not necessarily in lieu of .8102. Such addition increases the resistance' of the glass to devitrifination.

:TiQz may be incorporated in the glass with advantage to the optical properties and chemical durability. Both T 102 and ZrOztend to raise the refractive index of the glass more than'the other constituents but, whereas ZrO2 has only a slight effect on the dispersive index, T102 has .a strong depressing efiect on it. Hence, I prefer to use asmuch mm, between 4% and 15%, as will dissolve in the glass and .to add as much T102 as possible without unduly lowering the dispersive ndex- :Up t 02 may't s .be d ed.

The expansion coefficient for suitable scaling o h s anda d opti l crown lass will vary qm w a wit s t n po a d wit comp sition, and the newglasses will seal -satisfactorily H1 1 expan n c efi ci t ar etwe 3 X1 and 95 10- cm. per cm. per degree C.

The following compositions in weight percentage as calculated from their batches are given by way of example but not as limitations of the 1nvent1on:

Softening Point, C 650 664 675 666 667 662 Exp. O0efi.X10 83.3 .ss.s 88.3 86.4 90

Compositions 5 and 6 are particularly suitable for combination with standard optical crown glass to produce bifocal lenses.

It is characteristic of the new glasses that they contain a substantial amount of H02. Commercial ZrO2 sometimes contains a small amount of uranium as an impurity which is sufficient to cause fluorescence in bright light. This sometimes creates the appearance of an objectionable percentage basis it is not as effective as BaO. It fog or haziness before the eyes when spectacle lenses composed of such glasses are worn in strong light. I have found that the objectionable fluorescence can be prevented by melting the glass under reducing conditions or by the addition of a small amount of Sn02. The latter decomposes sufiiciently during melting to cause reduction of the uranium to a lower valence which does not fluoresce.

I claim:

1. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% Zr02, to 25% BaO, 3% to 15% Zn0, .5% to L120, 1% to Na20, the softening point being below 700 0., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10' and 95 10- cm. per cm. per degree 0. between 0 and 300 0. V I

2. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% Zr02, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 8% A120 the softening point being below 700 0., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 l0-" and 95 10-' cm. per cm. per degree C. between 0 and 300 C.

3. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% mm, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 15% CaO, the softening point being below 700 0., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10" and 95 10" cm. per cm. per degree 0. between 0 and 300 0.

4. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% Zr02, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na2O, up to 10% T102, the softening point being below 700 0., the refractive index (12D) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10-" and 95 l0' cm. per cm. per degree 0. between 0 and 300 C.

5. An ophthalmic glass which comprises 33% to S102, 1% to 7% B203, 4% to 15% Zr02, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 15% CaO and up to 10% T102, the softening point being below 700 0., the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coefiicient being between 33 10 and x10- cm. per cm. per degree C. between 0 and 300 C.

6. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% 2102, 0% to. 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 8% A1203 and up to 15% Ca0, the softening point being below 700 0,, the refractive index (nD) being between 1.57 and 1.70 and the thermal expansion coeflicient being between 83 10-' and 95 10 cm.

'per cm. per degree 0. between 0 and 300 0.

7. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% H02, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 8% A1203, and up to 10% T102, the softening point being below 700 0., the refractive index (11D) being between 1.57 and 1.70 and the thermal expansion coefficient being between 83 10-' and 95x10" cm. per cm. per degree 0. between 0 and 300 0.

8. An ophthalmic glass which comprises 33% to 60% S102, 1% to 7% B203, 4% to 15% Zr02, 0% to 25% BaO, 3% to 15% ZnO, .5% to 5% L120, 1% to 15% Na20, up to 8% A1203, up to 15% 02.0 and up to 10% T102, the softening point being below 700 0., the refractive index (11D) being between 1.57 and 1.70 and the thermal expansion coeflicient being between 83 10-" and 95 10 cm. per cm. per degree 0. between 0 and 300 0.

9. An ophthalmic glass which consists approximately of 37.5% S102, 4% B203, 5.5% Zr02, 20% BaO, 10% ZnO, 2% L120, 4.5% Na20, 2% A1203, 10% 0a0 and 4.5% T102.

10. An ophthalmic glass which consists approximately of 44.5% S102, 4% B203, "1% H02,

20% BaO, 7.5% ZnO, 2% L, 6% Na20, 2% A1203, 5% CaO and 2% T102.

WILLIAM H. ARMISTEAD. 

